The present invention is directed to nano optical sensors and photodetectors, and, more particularly, to such devices and their fabrication, employing self-assembly of molecules which modulate the electrical conductivity in a silicon nanowire.
Since the concept of molecular electronics was first proposed in 1974 by Aviram and Ratner (A. Aviram et al, Chemical Physics Letters, Vol. 29, pp. 277-283 (1974)), numerous studies have focused on probing single molecules in terms of using molecules directly as functional electric circuit components such as switches, diodes, or even transistors in replacement of conventional semiconductors, specifically, silicon. On another hand, the interaction of organic species with silicon surfaces remains a topic of considerable extent waiting to be explored, and the ability to tailor the surface electronic properties of silicon by organic or organo-metallic molecules poses a fascinating area hardly conceivable in the past. Cahen and coworkers (N. Zenou et al, ACS Sym. Ser., Vol. 695, pp. 57-66 (1998)) have pointed out that the electronic properties of silicon can be tuned by molecules with different electron-donating or electron-withdrawing groups on the surface. However, the molecules they discussed can only alter the silicon electronic properties once, not in a reversible or tunable fashion.
Thus, the reversible/tunable alteration of the electronic properties of silicon is needed.
In accordance with the embodiments disclosed herein, an optical sensor is provided. The optical sensor comprises:
(a) a silicon nanowire of finite length having an electrical contact pad at each end thereof; and
(b) a plurality of self-assembled molecules on a surface of the silicon nanowire, the molecules serving to modulate electrical conductivity of the silicon nanowire by either a reversible change in dipole moment of the molecules or by a reversible molecule-assisted electron/energy transfer from the molecules onto the silicon nanowire.
Also in accordance with the embodiments disclosed herein a method of making the optical sensor is provided. The method comprises:
(a) in either order, forming the silicon nanowire and the two electrical contact pads contacting the ends of the silicon nanowire;
(b) introducing the plurality of molecules to the surface of the silicon nanowire and allowing the plurality of molecules to self-assemble on the surface; and either
(c1) reversibly changing the dipole moment of the molecules to modulate the electrical conductivity of the silicon nanowire; or
(c2) reversibly transferring electrons between the molecules and the silicon nanowire.
The concept of molecular self-assembly is applied in attaching functional molecules onto silicon nanowire surfaces, and the requirement of molecule modification (e.g., hydroxy group in molecules) is minimal from the point view of synthetic difficulty and compatibility. Self-assembly will produce well-ordered ultra-thin films with strong chemical bonding on a surface that cannot be easily achieved by other conventional methods.
The incorporation of nano-imprinting technique to fabricate nano-silicon wires will be a practical route in mass production that most other nano-wire formation methods cannot achieve.
The present teachings offer a molecule-silicon hybrid electronic system, and utilize organic or organo-metallic molecules to modulate the semiconductor electronic properties in the nano regime, which could potentially produce optical sensing devices with much higher density and sensitivity.